Process of removing solvents from plastic colloids



Patented July 23, 1940 UNITED STATES PATENT OFFICE Hi PROCESS OF REMOVING SOLVENTS FROM 7 PLASTIC COLLOIDS Harry P. Bassett, Cynthiana, Ky., assignor to Meigs, Bassett and Slaughter, Inc., Philadelphia, Pa., a corporation of Pennsylvania No Drawing.

Original application March 4, 1930,

Serial No. 433,191. Divided and this applica- .tion October 13, 1937, Serial No. 168,841

8 Claims.

This invention relates to a process of removing solvents from semi-solid or plastic colloids and in its specific embodiment relates particularly to the removal of solvents from cellulose nitrate 51: plastic compositions such as Celluloid.

This is a division of my copending application Serial No. 433,191, filed March 4, 1930, which has become Patent No. 2,095,961.

The principal object of this invention is to prol'ii vide a simple and efficient process of removing solvents from plastic colloids whereby a product of superior quality is obtained and the removal of solvents is accomplished in a. relatively short period as compared with the time required in similar processes heretofore employed.

'An important object of this invention is to provide a simple, rapid and efficient process of removing solvents from nitro-cotton or similar plastic compositions which is substantially free ZQ fi'Om' the disadvantages commonly encountered in the processes heretofore employed-for similar purposes.

A further object of this invention is to provide a process of preparing Celluloid or other plastic sheets which are substantially free from integral dust specks and which are particularly adapted for use in making shatter-proof glass.

: A further object of this invention is to provide a process of forming sheets or other articles of a 39 cellulose'nitrate or similar plastic composition by extrusion or like means directly from a mass of the plastic composition.

Other objects and advantages of the invention will become apparent during the course of the 3 3 following description. I

' As is Well known, in the preparation of plastic colloids such as Celluloid, vulcanized fiber and the like, the basic materials employed are mixed with a suitable solvent, and generally a plasticiz- 6 ing'agent, and the mass worked up into the desired condition after which it becomes necessary to remove substantially all of the solvent or solvents present in order to prepare a finished n article from the material. In some cases the re- 45 'moval of the solvents is accomplished in several steps'which prolong the operating time of the process and involves substantial expense. The

present invention is designed to overcome to a large part these disadvantageous features of the 5i) processes heretofore employed.

r Other disadvantageous features are also encountered in the preparation of cellulose nitrate plastic compositions. As is well known, Celluloid and other nitro-cotton plastics are ordinarily 65X prepared by. suitably working-up collodion; a

plasticizing agent such as camphor, and a solvent such as alcohol, acetone, a mixture of ether and alcohol, or the like, driving off the excess of solvent, forming the article into a block or a mass of a particular shape and ageingthe finished article, i. e. removing the remaining solvent. In the formation of sheets of the plastic compositions, such as Celluloid sheets, the block of material is sliced or cut into sheets of the desired size and thickness, after'which the sheets 15 are aged. r

In the ageing of Intro-cotton plastic compositions, and particularly Celluloid sheets, theproducts are generally exposed to a drying atmos- I phere for arelatively long period of time. For {5* example, in ageing Celluloid sheets it is oftenthe practice to suspend the sheets in a drying chamber'for as long as from one to three weeks.- This air drying process, although widely practiced, is attended with numerous disadvantages,

particularly in-the caseof Celluloid sheets which are to be used in the making of shatter-proof glass. For example, the ageing plastics collect; a greater or .lessamount of atmospheric dust and this extraneous matter becomes an integral part f5 of the product during the drying process. More-: over, the plastic products tend to becomecasehardened rather than of homogeneous texture. Also, thin products such as Celluloid sheets tend: to curl and twist up during the ageing treatment whereby further treatment is required before thesheets are suitablefor use. These disadvantages, taken with the important disadvantagesof the excessive time required for ageing and the necesv sity of a specially constructed drying room, have: created a demand for a'rapid and simple process of ageing nitro-cotton or other plastics which is 1 free from these disadvantages. The foregoing disadvantages have also createda demand for a process of preparing finished. articles by=extrusion or like means directly fromthe basic mass of prepared plastic materialwhere-Ls by the intermediate steps between the mixing of the ingredients and the final formation of the 1 product are eliminated. :5

I have discovereda-simple process for remov-- ing solvents from partially finished plastic colloids such as vulcanized fiber, Celluloid, and. the like, which process may also be utilized to prepare finished plastic colloid products directly from the original mass of the plastic material... employed. While, as suggested, the process is. applicable-for use for) removingsolvents such, as zinc chloride from plastic compositions such as.

vulcanized fiber,. the; invention is particularlyeti ion its

sure at least as great as that within the colloid and gradually reducing the osmotic pressure of. the treating bath, preferablybythe'addition thereto of a miscible non-solvent of the plastic" composition which is capable".of'gmateriallyreducing the osmotic pressure of the-bath. It has been found that plastic colloids such as'a Celluloid mix may be extruded into a; treating bath of this character and a finished product'obtained by rei-i ducing the osmotic pressure of the'Joathwhereby Celluloid products, such as sheets, of supelior quality can be formed in a relatively shortpe'riod f ti .1- a w rm. was.

Various treating baths be,employed;:to,,se-

cure an; osmotic pressure'which is at :least as. great a's ,or greater than the osmotic. pressure within the colloid to .vbe,:treated-. For example, a

. concentrated ,aqueous, solution oficommon salt or, sugar maybe vemployed.. .:However, I .prefer tofemploy a solution of the desiredosmoti'c pressure of thesolventfv or one, of the ingredients of thesolventpresent-inthe plastic colloid and in the specific embodiment wherein Celluloid or; like nitror-cotton plastic :colloidsare being treated I prefer to employ a solution of alcohol; 7 The osmotic;pr,essure'off,this treatingbath may be reduced by.replaci.ng, the solutionwith any miscible nonsolvent of the colloid whichgiscapable of reducing the 'osmotic pressure of thebathtvj However,

' the interest of cc0nomy;,-I preferwtoemploy water togreduce the osmotic pressure, of the bath.

.eInianattempt .to. remove the remaining. solvents fromvpartially.;.finished nitro-cotton or other plasticsin a rapid and'eflicient manner, the' expedient of immersingthe productsetlo be treated in; '.water .was practiced, it being recognized that the solvents ordinarily used are readily soluble in-or miscible ,with and have a certain ailinity for water. ,I-Iowever, this expedient was not, successful forthereason that although thesolvent wasgremoved, the composition became substantially ,opaquedue to a'discolorationwhich is commonly-termed "blushingf. I This proved ;to be particularly disadvantageous :in connection with the I preparation -.of Celluloid-sheets designed for use in {the manufacture of shatter proof, glass,"

in which type of glass a sheet of Celluloid is placed between and united to two piecesof, glass; However,;fthe solvent was satisfactorily'removed by the water treatment and this method wasypura sued. with a view of overcoming the, blushingl effect produced. 1

;After repeated experiinents,-it was fouhdthat the solvent or solvents could be satisfactorily re-jmoved and the blushing avoided by immersing the partially finishedarticle fora suitable length of time in abath of water. containing .a suitable material in a sufficient amount to raise the .osmotic pressure of thebath to'tha't ofor'Ygreater than the'osmotic pressure within the plastic material; iand'graduallyreplacing the added mate- .rial in-"the treatin'g bath with water or other ,miscible nonsolvent iof the plastic composition adaptedito reduce'the: osmotic pressure materially below that withinthe colloid. In "the .case of Celluloid, it was found advantageous to add a sub-1 stantial proportion sayl from '20- to per cent. 3

of alcohol to the treating bath and gradually replace this with water.

Following this procedure, Celluloid sheets of an inch thick were found to be completely aged in five hours without any blushing of 5 the sheets. Moreover, this,1-'ageing1' process resultedin the formation of pr'oducts of substantially homogeneous texture which were wholly free from dust and substantially free from the 'this'imp'r'oved procedure has been utilized with great practical success particularly in the ma'nu-,

facture of Celluloid-sheets designed to be used in making shatter-proof glass.

16 In addition to providing an eflicient means of ageing plastic; colloids the process has been found to bejof. great practical value in forming finished... products from plastic colloids as originally'mixed for use. invention; the mixed material,'--such jasamlastic Celluloid mix was extruded in sheetform; intfo;1 the treating bath of the desired osmoticpressure and :the bath gradually; replaced withj -water-;y The sheets producedwere of superior quality and; 25 their productionwasiobtained in avery small fraction of time which is now required for the; production of similar articles accordin j to the; methods commonly employedl Moreover, -,this modification of the process; effectsawmateijial so economy since the intermediate steps of forming;

' a-partially prepared product are 'eliminated.

. For the purpose of describing the preferred; practice of my process the procedure of ageingpartially prepared Celluloid sheets will :be out fgu lined. However, this procedure should be considered as illustrative only sincevitis to. be '1] derstood that the same general' proce dure be followed in connection with other partially, prepared plasticcolloids, such as :those referr to above, and may also be followed where a mix;- of the plastic colloid material is directly formed into a finished product as bymeans ofextrusibn; t a ure .of C' u qid Shee s. th compressed block of freshly prepared :Celluloid. which has been formed in the usual manner-is, sliced or out according to any conventional 'proc ess into sheets of the desired size andthiclgness. These sheets will contain .a certain amount of residual solvent such as ether and alcohol, or the like,- and for the purpose of removing such resid-; ual solvent the freshly preparedsheets are immersed in a suitable tank containing amaqueous solution of alcohol, or other. nonsolvent solution, having an osmotic pressure slightly greater than: 5g the osmotic pressure within the Celluloid. When alcohol in water is employed, Ivhave foundrit;,lad vantageous to ,employa solution cont ai.ning;approximately 20 per cent. Of the alcohol. percentage may be widely increased or decreased 6,0 according to the osmotic pressure within the Cell; luloid but the use of a greater amount of alcoholl is generally not recommended for thereason that no substantially improvedresults are obtained and the process is rendered more expensive b31135 this use of an excessive amount=;of -aleo1ib1 1 1 the preferred practice, the, Celluloid sheets are suspended in any suitable manner from support- 1 ingj frames in a 20 per cent. aqueoussolution of ri alcohol and this solution is gradually replaced by; water, the replacement requiring about five hours 7' in the case of sheets. 3 of an inch thick.-.--, A: temperature corresponding to normal atmos-i: pheric temperature has beenfound to be tmost satisfactory for commercial useb'ut'temperatures-175i In this modification of the g0 as high as 40 to 50 C., and even higher, may be used commercially with good results, but the lower the temperature, the less loss of alcohol and formation of defects, such as bubbles, haze and the like.

During the ageing process, as described, the residual solvent in the freshly prepared material is taken up by the water with the result that, after the relatively short period of treatment set forth above, substantially all of the solvent is removed and a finished product of substantially homogeneous texture is, produced. The surface liquid need only be removed before the product is in condition for use as desired.

A modification of'this process which is particularly advantageous for use on a large commercial scale and which is productive of excepe tionally good results consists in the employment of a plurality of tanks, say six in number, in which the percentage of alcohol is progressively decreased. For example, the first tank may contain a solution containing approximately 20 per cent. alcohol into which the Celluloid or other plastic is placed. This solution is replaced gradually by water and allowed to overflow into tank #2, which containsa previous charge of Celluloid, tank #2 overflowing into tank #3 and so forth to tank #6. By this time, the plastic in tank #1 is aged sufficiently and is removed and a fresh charge placed therein. Tank #2 then receives the water and in a short time, say one hour, more is aged and plastic is removed, #1 becoming #6 and #2 becoming #1, and so forth in a countercurrent manner.

The above method is most practical but the countercurrent principle may also be used by employing a series of tanks in which the percentage of alcohol progressively decreases and moving the plastic from time to time at stated intervals. According to this modification, the freshly formed sheets are dipped into the treating tank containing the largest percentage of alcohol where they are left for the desired period of time after which they are removed to the intermediate treating tanks where they are immersed for corresponding periods after which they are introduced into the final treating tank. As will be apparent, the time of treatment in the various tanks may be widely varied according to the nature of the particular articles under treatment and the amount of residual solvent present therein.

Another form of continuous process may be provided by the use of an elongated tank into the entry end of which is caused to flow a current of alcohol and into the discharge end of which is caused to fiow a current of Water so that the strength of the alcohol progressively decreases toward the discharge end of the tank. In this modification the sheets may be moved by suitable mechanism from the inlet to the discharge end of the apparatus.

In the modification of the process wherein a plastic composition, such as Celluloid, is to be extruded or otherwise formed directly into sheets or other masses of a particular shape, any conventional extruding or like machine may be employed and the extruded mass is introduced into the treating bath where it is preferably given a similar treatment to that described above. When the residual solvent has been removed during the process the sheets or other articles are removed and freed from surface liquid after which they may be used directly or subjected to any finishing steps as may be desired.

While I have described in detail the preferred embodiments of my invention, it is to be understood that the details of procedure may be Variously modified without departing from'the spirit of the invention or the scope of the subjoined claims.

I claim:

1. A process of the character described which comprises immersing a freshly formed cellulose ester plastic composition in a bath comprising an aqueous solution of sodium chloride and having an osmotic pressure at least as great as that which said plastic composition, and thereafter reducing the osmotic pressure of the bath below that within said plastic composition.

2. A process of removing residual solvent from freshly formed Celluloid which comprises immersing the same in a concentrated solution of sodium chloride, and thereafter subjecting the Celluloid to the action of an aqueous bath of reduced sodium chloride concentration.

3. A process of the character described which comprises the steps of extruding a cellulose ester plastic composition mix into a bath comprising an aqueous solution of sodium chloride and having an osmotic pressure at least as great as that within said plastic composition, and thereafter reducing the osmotic pressure of the bath below that within said plastic composition.

4. A process according to claim 3 in which said mix is a Celluloid mix.

5. A process of the character described which comprises the steps of extruding a cellulose ester plastic composition mix into a concentrated solution of sodium chloride, and passing the plastic composition into an aqueous solution of sodium chloride of reduced concentration.

6. A process according to claim 5 in which said mix is a Celluloid mix.

7. In a continuous process of producing a cellulose ester plastic wherein the plastic, containing residual solvent, is initially formed and the plastic is subsequently treated to remove residual solvent therefrom, the improvement in the solvent removal procedure which comprises continuously passing the freshly formed plastic through successive solvent-removing baths in which, during continued practice of the process, an accumulation of solvent occurs, the bath through which freshly formed plastic is initially passed comprising a concentrated solution of sodium chloride and also containing removed sol- Vent, the succeeding bath being a sodium chloride bath capable of removing additional amounts of solvent and containing a lower concentration of removed solvent than the first named bath.

8. In a continuous process of producing a cellulose ester plastic wherein a solution of a cellulose ester plastic composition is extruded through a shaping device and the extruded product treated to remove solvent therefrom, the improvement which comprises continuously passing the extruded product through successive solventremoving baths in which, during continued practice of the process, an accumulation of solvent occurs, the bath through which the extruded product is initially passed comprising a concen-' 

